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Textile factories are usually batch plants. Their high freshwater consumption and large emissions of toxic wastewater present a threat to water availability and public health. Wastewater minimizati...

Many countries are currently facing a severe water crisis. Further, in various industrial sectors, small and medium enterprises operate multistage, multiproduct batch processes that require large quantities of water. This work is motivated by the inability of such enterprises to deploy complex water-reuse strategies since their plants are neither well instrumented nor automated. The design and operational strategies of water reuse networks for multistage, multiproduct batch processes is inherently challenging due to the underlying discontinuities and other nonlinearities. In this paper, we propose an easy-to-implement water-reuse strategy that utilizes intermediate storage tanks with finite capacities. The strategy relies on a simple heuristic that maps discharge from specific stages to be stored in corresponding tanks. A fallback sequence is also provided in case the tank cannot accommodate the entire discharge volume. An analogous scheme for reusing water from the tanks in appropriate process stages is also proposed. In this paper, we demonstrate using a textile industry case study that this simple reuse strategy can result in significant water savings. For this, we develop an optimal production schedule using a genetic algorithm that simultaneously minimizes production makespan and the freshwater consumption. Our results show that for a set of 4 products with up to 14 production stages, 76% of the freshwater could be reduced if 13 tanks can be deployed. Even with 2 tanks, the proposed strategy results a 42% reduction of the freshwater requirements.

Stringent environmental regulations and economic expansion in the recent decades has justified the need for sustainable water usage in the process industry. This work presents a mathematical formul...

Water conservation is becoming increasingly important due to increasing demand and stringent environmental legislations. This work proposes a dynamic programming (DP) method for the design of water...

This work presents a mathematical framework for optimizing water-energy nexus during shale gas production, processing, distribution, usage in power generation, and transmission of produced power. The framework entails a superstructure-based mathematical formulation. Regeneration is achieved using membrane distillation (MD), whereby the treated water can be reused at the next fracturing operation. The developed model incorporates a detailed design model of MD to account for the design specifications and energy requirements of the water regenerator. Hence, water, energy, operating and/or capital cost are optimized simultaneously. The study considers natural gas as fuel for commercial, industrial and residential customers, as well as for electric power generation, with the goal of maximizing the overall profit. The resultant model is applied to a case study, which is a representative of Marcellus shale play. The approach results in 23.2% reduction in freshwater utilization, 18.6% reduction in the freshwater cost and 42.7% reduction in the energy requirement of the regenerator. The energy requirement for regeneration is 160 × 103 kJ/m3 of water. The results indicate that the cost incurred in the network involving wet gas is 41.76% higher than the network involving dry gas due to the processing requirement of wet gas.

The rising cost of freshwater and wastewater treatment drives the development of systematic methods for water integration in batch plants. In addition, in batch processes, production rescheduling can further reduce freshwater consumption and wastewater generation. In this work, a design procedure for the synthesis of batch water networks, based on a flexible scheduling framework, is presented. Within the procedure a match ranking matrix is utilized to prioritize the matches between water sources and sinks. Based on the ranking, batch water networks can be designed while considering the time-dependent nature of batch processes. The design of a batch water network and a production schedule can be obtained simultaneously with the objective of minimizing freshwater consumption. In this work two examples are considered to demonstrate the feasibility of the proposed method. In the first example a regenerator with a fixed outlet concentration is incorporated to treat wastewater for further reuse. In the second example a batch plant with multiple contaminants is presented, in which a fixed removal ratio regenerator is employed. The results of these two examples demonstrate that the proposed method is a simple, effective approach for the design of batch water network with a flexible scheduling framework.

Application of fiber-reinforced composites (FRC) in industrial and clinical improvement is evolving amid growing demand in all areas of innovative technology. Substantial benefits of FRCs have been adapted in sciences and engineering with possibility of further exploration. Part of the attractive properties of these composites is their renewability and biodegradability. These two salient properties have been adapted in automobile and aerospace industries to evolve automobile part and rotor blades formation respectively. The implication of FRCs in key components replacement has significantly reduced the entire payload of body weight system of either automobile vehicle or aircraft system with overall reduction in energy demand in these systems. Further to this, FRCs have enjoyed substantial patronage in plastic formation and all manner of industrial need. One may not be able to count huge number of FRCs in structural and building construction with substantial reduction in the cost of procurement of these materials. The foray into green materials have evolved electrically conductive fiber-reinforced materials which have been reported to be suitable for drug delivery systems, biomedical implants and tissue engineering. In several published papers, findings have revealed the application of FRCs in dental and medical implants. In this chapter, extensive works were done to x-ray the involvement of fiber-reinforced composite in medical and industrial application. Taking into consideration the voluminous nature of fiber reinforced materials, this work restricted the scope of this study to exclude metallic component of fiber reinforced composite while the attention was majorly on natural fiber reinforced composite. The impact of biodegradable materials in regenerative medicine also formed key area in this work highlighting their significance and shortcoming as reported in clinical practise. Concluding part of this chapter dwelled on the prospects and viabilities of the materials while considering their limitations in clinical works.

Water minimization in the process industry is becoming increasingly important due to increasingly stringent environmental legislation, especially for batch plants. This work proposes a dynamic programming (DP) method for the optimal design of water-using networks in batch plants. DP is a powerful framework for dealing with a large spectrum of multistage decision-making problems and has been applied in numerous chemical engineering problems. The proposed methodology is explained as follows. Firstly, based on the start time and end time of each operation, the whole process is divided into N stages. Secondly, the water requirement of water-using units in each stage is satisfied and the state of stored water and wastewater generation is determined. The backward procedure of DP is used to solve the DP problems. The target of freshwater consumption of the process and the optimal design of the water network are obtained simultaneously. In order to display the versatility of the proposed approach, four examples from literature are considered. Example 1 is a completely batch process with a fixed flowrate problem. Example 2 is a hybrid batch water system comprising various modes of operations and operating patterns. Example 3 is a fixed-mass load problem with a regeneration unit, while example 4 considers the batch water network design with multiple contaminants. The results obtained in this work were comparable with the results from literature, implying that it can be applicable to both mass transfer-based and non-mass transfer-based batch water networks.

Water and wastewater services are essential utilities in industrial parks. However, in many parts of the world, pressure from climate change, resource depletion, and economic growth results in water stress that can affect operations of industrial systems. The theme of this Virtual Special Issue (VSI) is to introduce interdisciplinary contributions to discuss topics related to sustainable water management in industrial parks. Rigorous conceptual, analytical, and quantitative approaches are needed in order to support such management efforts by eco-industrial park (EIP) managers, policy makers, process engineers, scientists, and other professionals. Management and continuous optimization of industrial water use are essential climate change adaptation strategies to achieve sustainable growth.

A superstructure-based optimisation model for the CO2 capture process using an N2-selective and CO2-selective membranes is presented. The model automatically selects either of the membranes for each membrane stage to have a hybrid membrane CO2 capture process. The superstructure embeds numerous process routes and allows the collection of product streams and residue streams from either the retentate side or permeate side of the multi-membrane stages. This results in novel process flowsheets for post-combustion CO2 capture using membrane technology. In the study, the optimisation of carbon capture by an all N2-selective membrane process is also carried out. At 90% recovery and 95% product purity, the multi-stage optimisation of the N2–CO2 hybrid membrane process reduces the total membrane area by 46% and the cost of capture by 14% compared to the optimised CO2-selective membrane process.

Energy minimisation in batch plants has garnered popularity over the past few decades, leading to direct and indirect heat integration techniques being formulated for multipurpose batch plants through the utilisation of mathematical formulations and insight-based methods Some mathematical formulations utilise predetermined scheduling frameworks which may result in suboptimal results, whilst other formulations only use one heat storage vessel which may cause limitations in the plant. The work presented in this manuscript is aimed at minimising energy consumption in multipurpose batch plants by exploring both direct and indirect heat integration through multiple heat storage vessels. It investigates the optimal number of heat storage vessels as well as design parameters, i.e. size and initial temperature of vessels. The cost of the heat storage vessels is considered within the model. The model is applied to two case studies resulting in significant increase in profits.

The dairy sector in India, being the largest milk producer in the world, consumes substantial amounts of water annually. This industry is, therefore, likely to affect water sustainability in India in the near future. Amul Dairy, is the largest food brand in India and as such consumes large amounts of water annually. The cleaning-in-place (CIP) processes at Amul Diary accounts for nearly 75% of the total water consumption. The raw milk receiving and processing department (RMRD) requires nearly 90% of the total water used in CIP. This work, therefore, investigates the water usage in Amul Dairy and identifies the prospects of water reuse by using optimization techniques for minimizing water usage in the RMRD. This was achieved by treating the wastewater from the RMRD plant by means of a reverse osmosis (RO) membrane in order to allow opportunities for regeneration–reuse/recycling in the CIP process. An overall mixed-integer nonlinear programming (MINLP) framework was developed that simultaneously evaluates both water recycle/reuse and regeneration reuse/recycle opportunities. The model applied to the CIP process in the RMRD plant resulted in 33% reduction of freshwater consumption and 85% reduction of wastewater generation.

The minimization of water in batch plants through process integration has been well established in the literature. While many existing methods have relied on a fixed batch schedule, a few have employed variable production schedules. Nevertheless, methods employing variable schedules in fixed mass load problems have assumed that water-using operations (washing) are sequence independent. This paper presents a mathematical formulation for the simultaneous optimization of batch production and minimization of wastewater in fixed mass load problems. Wastewater minimization is achieved by exploring the sequence of tasks in a unit. The effectiveness of the formulation was demonstrated using three case studies. The results show that even without process integration, water usage can be minimized through the appropriate selection of task sequences in a unit. Reductions in water usage of 33% and 48.8% were observed in case study I and case study II respectively.

Most scheduling methods are limited to the short-term scheduling case and solution of problems over long time horizons may prove challenging or impossible with these methods. Including additional considerations such as Heat Integration further complicates the problem. A model for the simultaneous optimisation of the schedule and energy usage in heat integrated multipurpose batch plants operated over long time horizons has been presented. The method uses a cyclic scheduling solution procedure. The proposed model includes indirect Heat Integration via heat storage, rather than just direct Heat Integration. This has not been considered in long-term Heat Integration models in current literature. Both the heat storage size and initial heat storage temperature are also optimised. The solution obtained over 24 h using the proposed cyclic scheduling model with direct Heat Integration for a multipurpose example was compared to the result obtained from the direct solution and an error of less than 6% was achieved.

Water management in hydraulic fracturing is an important issue as wastewater management is the key driver of water-related costs. Selection of appropriate water management options in hydraulic fracturing involve consideration of many factors, which includes operational, environmental and economic factors. This study looks at the role of efficient scheduling framework together with low-pressure membrane technology in maximizing wastewater reuse in hydraulic fracturing with focus on ultrafiltration (UF) membrane technology. The study considers detailed ultrafiltration model in order to evaluate the sustainability of the system in terms of energy consumption and associated costs. The study also looks into the feasibility of using the gas that would otherwise be flared to generate electrical energy for the membrane system via an onsite gas generator. The application of the proposed model in a case study results in 21.4 % reduction in the amount of water required for fracturing and 10.3 % reduction in the amount of energy needed by the regenerator. The system consumes 0.109 kWh/m3 of energy at an operating pressure of 3.69 bar. This indicates a very low-energy consumption compared to a typical energy requirement for wastewater reclamation which usually ranges between 0.8 and 1.0 kWh/m3 for membrane filtration. The study indicates the possibility of reducing the operating cost of the regeneration network by 61 % if the electrical energy needed is generated onsite using the gas that would otherwise be flared.

Significant opportunities for energy savings in batch plants exist through Heat Integration of intermittently-available material transfer streams between processing and storage units. Such opportunities may, however, be limited by the structure of the process flowsheet and the scheduling in place. This work presents results obtained when the design, scheduling and Heat Integration of multipurpose batch plants are carried out simultaneously. A rigorous stream-task-oriented scheduling formulation is presented, which enables explicit description of the movements of the intermittently-available streams. This thorough treatment of streams opens up more degrees of freedom than realised in previous stream Heat Integration formulations. On such a basis, design and Heat Integration constraints are added, to result in a mixed integer nonlinear programming formulation. The optimisation objective is to maximise annual net profit, which is a trade-off between production throughput, capital costs, and operational costs arising from hot and cold utility consumption. When applied to a literature example, results show higher annual net profit and reduction in utility costs by as much as 15%, compared to when each of the design, scheduling and Heat Integration steps are carried out in sequence.

This study presents a superstructure based mathematical model for the optimisation of the CO2 capture process from flue gas by use of a fixed site carrier membrane. The goal is to determine the optimum process flow sheet that gives the minimum total cost whilst achieving 90 % recovery and 95 % purity of CO2. The model is applied to a case study of a coal-fired power plant to assess the merits of the optimisation and the feasibility of implementing the membrane at a large scale. The membrane properties used in the simulation are obtained from the literature. This work involves the use of an accurate expression for CO2 permeance of CO2 in a poly-amine fixed site carrier membrane in relation to CO2 partial pressure. This allows pressure to be a variable in the optimisation problem. The use of water vapour as sweep is also explored and compared to the vacuum-driven only process. The application of the model results in a decrease in membrane area requirement of 46 % and a decrease of 13.6 % in the cost of CO2 avoided compared to a pre-determined two stage cascade process operating at uniform pressure. The results show that the use of water vapour as sweep in conjunction with vacuum pumps on the other membrane stages is more economical compared to the use of vacuum pumps only.

In process systems engineering, it is critical to design an effective and optimized process in a short period with minimum experimental trials. However, improvement of some process variables may deteriorate some other criteria due to conflicting regions of factor interests for optimal solution in multi-objective optimization (MOO) processes. Here, the global optimization of an adsorption case study with conflicting optimal solutions based on multi-objective Response Surface Methodology (RSM) design is facilitated with the implementation of BARON solver based on General Algebraic Modeling System (GAMS) with identical factor variables, levels, and model equations. RSM suggested fifteen different optimum settings of which the validation is quite expensive and onerous, whereas GAMS suggested a single optimum setting which makes it more economically viable especially for large scale systems. In addition, the GAMS-based optimization provided more accurate and reliable results when experimentally validated as compared to the RSM-based solution.

The water-energy nexus considers the relationship between water and energy resources. The tightening environmental regulations and social pressures have made it necessary to develop processes that are conservative with respect to both these resources. In the first part of this series, a multi-contaminant electrodialysis (ED) model was developed. In this second part of the series, the application of the developed ED model for the partial purification of contaminated water within a water network synthesis (WNS) and optimization problem is explored. The optimization model is based on a superstructure framework, where the objective is to minimize freshwater consumption, wastewater production, energy consumption and the operating and capital costs involved in the process integration. A comparison is made between the framework presented in this manuscript and the more common black box model, which simplifies regeneration units to linear expressions. The results show that the black box approach can lead to inaccuracies of up to 85% in the costing of regeneration units. ED optimization performed within the WNS problem results in a more comprehensive design than if the design is developed as a standalone model. Furthermore, it is shown that there are significant environmental and financial benefits in the simultaneous minimization of water and energy in water networks. When applied to a pulp and paper case study, the integrated approach resulted in 38% reduction in total freshwater consumption and 67% savings in wastewater treatment costs.

Electrodialysis (ED) is a membrane process commonly employed for the desalination of brine or water contaminated by ionic components. The driving force for desalination is the potential difference between the contaminated and purified water. Despite its ability to produce ultra-pure products, the application of electrodialysis is exceeded by other treatment processes, due to its energy intensity. Energy consumption in ED is dependent on the physical characteristics of the unit. In this respect, it is possible to promote the use of electrodialysis by optimizing the process, making it more energy efficient. This can be done by developing an optimization framework for the process. Existing electrodialysis design models, based on current density, cater mainly for the desalination of brine. This paper presents a detailed derivation for a single stage electrodialysis design model, suitable for treating a binary mixture of simple salts. A simplified formulation is also presented, based on the assumption that the conductivity of the solution is constant over the entire unit. This simplifying assumption enables more versatile application of the ED design model with background processes. Using a pulp and paper case study, a comparison is done between the two models, indicating a deviation of less than 2% in all key variables. It is therefore possible to reliably use either of the models interchangeably, depending on the available information and the background process under consideration. Both models presented are mixed integer nonlinear programs (MINLP) solved using a combination of DICOPT and BARON solvers in GAMS®.

Water and energy are key resources in the process industry. The increasing pressure on freshwater and energy resources coupled with stringent environmental regulations on effluent discharge limits have called for innovative designs for sustainable use of water and energy. This can be achieved through process integration techniques that are environmentally benign and economically feasible. This work proposes a robust water network superstructure optimization approach for the synthesis of a multiregenerator network for simultaneous water and energy minimization. Two types of membrane regenerators are considered for this work, namely, electrodialysis and reverse osmosis. In each of the membrane regenerators, a detailed design model is developed and incorporated into the water network model. The detailed model presented in this work is compared to the more common “blackbox” model, which uses linear expressions to represent costs of regeneration units. The results show that the “blackbox” model gives inaccurat...

In this first of a series of two papers, the effects of varying steam levels on the total steam flowrate are analyzed mathematically for the traditional parallel configuration as well as for the case of hot liquid reuse. It is demonstrated that in the case of parallel heat exchangers utilizing only latent heat, a minimum total steam flowrate is obtained by optimally selecting steam levels, but that in the case of hot liquid reuse, introducing multiple steam levels increases the minimum total steam flowrate attainable under those conditions. The flowrate attained utilizing hot liquid reuse, however, remains lower than when only utilizing latent heat. It is concluded that the lowest steam flowrate is attained using hot liquid reuse and only a single level of steam, but that the presence of additional steam levels resulting from turbines requires a more holistic approach to the synthesis of steam networks.

In this first of a series of two papers, the effect of varying steam levels on the total steam flowrate within steam systems is analysed mathematically for the traditional parallel configuration as well as for the case of hot liquid reuse. It is demonstrated that in the case of parallel heat exchangers utilising only latent heat, a minimum total steam flowrate is obtained by optimally selecting steam levels, but that in the case of hot liquid reuse, introducing multiple steam levels increases the minimum total steam flowrate attainable under those conditions. The flowrate attained utilising hot liquid reuse, however, remains lower than when only utilising latent heat. It is concluded that the lowest steam flowrate is attained using hot liquid reuse and only a single level of steam, but that the presence of additional steam levels resulting from turbines requires a more holistic approach to the synthesis of steam networks.

The shrinking supplies of freshwater globally, coupled with strict environmental regulations, have driven the manufacturing industry towards sustainable water management for the minimisation of freshwater intake and wastewater generation. By using process integration and its enabling tools, this work considers the synthesis of an optimal water network with multiple regeneration capabilities. Development of the proposed framework is achieved by embedding a subnetwork of detailed electrodialysis models within a water network. Based on a superstructure and fixed flowrate, the optimisation problem is formulated as an MINLP model and solved in GAMS/DICOPT. To demonstrate the applicability of the proposed mathematical model a literature case study on a pulp and paper plant is presented and the results indicate a potential of 12% savings in freshwater intake, 16% reduction in wastewater generated and a 14% saving in the total annualised cost for the entire network.

Fossil fuels have earned a reputation as unsustainable sources of energy, due to the release of carbon emissions that are attributable to global warming. To overcome the extensive release of carbon emissions into the environment, different approaches are being explored to produce energy, by replacing non-renewable fuels with renewable energy. Additionally, many countries across the world are emerging as water-scarce countries, due to the vulnerability of freshwater supply. This work, therefore, focuses on the design and synthesis of a hybrid electrolyser-fuel cell system to generate hydrogen and freshwater from seawater. The proposed system is designed to be integrated with a background process that requires both power and water. It has the potential to reduce the burden on freshwater sources and carbon footprint of background processes, as well as produce power. A one-dimensional, mathematical model is developed for a continuous hybrid seawater electrolyser-fuel cell system operated at steady state. The model determines the optimal operating conditions in terms of temperature, current density, electrode thickness and humidity, as well as the performance of the system through the activation overpotential, diffusion overpotential, ohmic overpotential and the open-circuit voltage. GAMS/BARON is used to optimise the hybrid system. Furthermore, a techno-economic evaluation is conducted to determine the viability of the system. Results indicate that an overall power conversion efficiency of 41.2%, and a freshwater recovery rate of 48.2% is achieved.

In view of sudden changes in climatic weather conditions, resulting in variation and dislocation of environment and biodiversity, there has been new initiatives in automotive industry to develop a lighter and sustainable materials to mitigate fossil fuel demand in transport system and improve the overall vehicular part maintenance. In almost all the developed part of the world, major car manufacturer have evolved new composite materials to replace original equipment body as government regulations become stricter in response to worsening environmental degradation. The concept of this paper is to report findings on new material formation using hand lay-up as manucturing technique. In this paper, part of the novel approach in transport system is the possibility of payload reduction through the adaptation of new materials as external and internal parts of the system. Five materials were processed in this work with two specimens oriented at varying degree (30° and 60°) while the other three were without degree of orientation. The payload of these materials were estimated using all the conceptual parameters of a typical vehicle system and the findings from this research showed that 10%wt. of fibre at 30° orientation in the matrix, will possibly offer the lowest panel weight as presented in this paper. This study may be investigated further with a view to test the energy consumption of this new material via-a-viz other reinforced composite materials.

This work presents a mathematical model for the simultaneous optimisation of water and energy usage in hydraulic fracturing using a continuous time scheduling formulation. The recycling/reuse of fracturing water is achieved through the purification of flowback wastewater using thermally driven membrane distillation (MD). A detailed design model for this technology is incorporated within the water network superstructure in order to allow for the simultaneous optimisation of water, operation, capital cost, and energy used. The study also examines the feasibility of utilising the co-produced gas that is traditionally flared as a potential source of energy for MD. The application of the model results in a 22.42% reduction in freshwater consumption and 23.24% savings in the total cost of freshwater. The membrane thermal energy consumption is in the order of 244 &times, 103 kJ/m3 of water, which is found to be less than the range of thermal consumption values reported for membrane distillation in the literature. Although the obtained results are not generally applicable to all shale gas plays, the proposed framework and supporting models aid in understanding the potential impact of using scheduling and optimisation techniques to address flowback wastewater management.

Energy minimisation in batch plants has garnered popularity over the past few decades, leading to direct and indirect heat integration techniques being formulated for multipurpose batch plants through the utilisation of mathematical formulations and insight-based methods. Some mathematical formulations utilise predetermined scheduling frameworks which may result in suboptimal results, whilst other formulations only use one heat storage vessel which may cause limitations in the plant. The work presented in this chapter is aimed at minimising energy consumption in multipurpose batch plants by exploring both direct and indirect heat integration through multiple heat storage vessels. It investigates the optimal number of heat storage vessels as well as design parameters, i.e. size and initial temperature of vessels. The cost of the heat storage vessels is considered within the model. The model is applied to two case studies resulting in significant increase in profits.

Strict environmental regulations and social pressures have created the need for water and energy minimization in the process industries. Therefore, this work looks at the incorporation of a detailed reverse osmosis network (RON) superstructure within a water network superstructure in order to simultaneously minimize water, energy, operation, and capital costs. The water network consists of water sources, water sinks, and RO units for the partial treatment of the contaminated water. An overall mixed-integer nonlinear programming framework is developed that simultaneously evaluates both water recycle–reuse and regeneration reuse–recycle opportunities. The solution obtained from optimization provides the optimal connections between various units in the network arrangement, size and types of RO units, booster pumps, as well as energy recovery turbines. The paper looks at four cases to highlight the importance of including a detailed regeneration network within the water network instead of the traditional “bla...

Presented in this paper is a mathematical technique for simultaneous heat integration and process scheduling in multipurpose batch plants. Taking advantage of the intermittent continuous behavior of process streams during transfer from one processing unit to another, as determined by the recipe, the presented formulation aims to maximize the coincidence of availability of hot and cold stream pairs with feasible temperature driving forces, while taking into consideration process scheduling constraints. Contrary to similar contributions in published literature, time is treated as one of the key optimization variables instead of a parameter fixed a priori. Heat integration during stream transfer has the added benefit of shortened processing time, which invariably improves throughput, as more batches are likely to be processed within a given time horizon, compared to conventional heating and cooling in situ. Application of the proposed model to a case study shows improvements of more than 30% in energy savings and up to 15% in product output.

Water minimization in the process industry is becoming increasingly important in chemical industries, especially for the batch plants. This work proposes a dynamic programming (DP) method for the optimal design of water-using networks in batch plants. The proposed methodology is explained as follows. Firstly, water-using units are transformed into the water sources and sinks with specific water requirements and time constraints. Secondly, based on the start and end time of each operation, the whole process is divided into N stages. Also these water sources and sinks are arranged in the diagram with time or stages on the horizontal axis and the concentration on the vertical axis. Thirdly, the backward procedure of DP is used to solve the problems based on the insights of diagram. The target of the process and optimal design of water network are obtained simultaneously. In order to display versatility of the proposed approach two examples from literature are taken into account. Example 1 is a completely batch process with a fixed flowrate problem. Example 2 is a hybrid batch water system comprising various operations (fixed load and fixed flowrate) and operating models (completely batch and semi-continuous). The obtained results match with the results from literature, implying that it can be applicable to design optimal batch water networks.

Presented in this contribution is a formulation that addresses optimization of both water and energy, while simultaneously optimizing the batch process schedule. The scheduling framework used in this study is based on the recent and efficient formulation. This formulation has been shown to result in a significant reduction of computational time, an improvement of the objective function and leads to fewer time points. The objective is to improve the profitability of the plant by minimizing wastewater generation and utility usage. From a case study it was found that through applying only water integration the cost is reduced by 11.6%, by applying only energy integration the cost is reduced by 29.1% and by applying both energy and water integration the cost is reduced by 34.6%. This indicates that optimizing water and energy integration in the same scheduling framework will reduce the operating cost and environmental impact significantly.

The focus of this article is on the dependence between water and energy in industry and the way these resources can be managed in an integrated and more sustainable manner. The fundamental methodology supporting the concept of simultaneous management of water and energy is the process systems approach guided by deep understanding of the simultaneous mass and heat transfer, considering phase and pressure changes. Special attention in this case is paid to the utilization of the latent heat of water evaporation and condensation (allowing for water and heat recycling). The article takes a new view of water solutions management, especially when processes experience difficulties for direct heat recovery. The article also highlights the links between water management, heat recovery, process efficiency improvement, and capacity de-bottlenecking, which bring additional positive impact of proposed methodologies. The advantages of efficiency improvement, water saving, and improved environmental impact of proposed so...

This study has applied the concept of the hybrid PAC-UF process in the treatment of the final effluent of the palm oil industry for reuse as feedwater for low-pressure boilers. In a bench-scale set-up, a low-cost empty fruit bunch-based powdered activated carbon (PAC) was employed for upstream adsorption of biotreated palm oil mill effluent (BPOME) with the process conditions: 60 g/L dose of PAC, 68 min of mixing time and 200 rpm of mixing speed, to reduce the feedwater strength, alleviate probable fouling of the membranes and thus improve the process flux (productivity). Three polyethersulfone ultrafiltration membranes of molecular weight cut-off (MWCO) of 1, 5 and 10 kDa were investigated in a cross-flow filtration mode, and under constant transmembrane pressures of 40, 80, and 120 kPa. The permeate qualities of the hybrid processes were evaluated, and it was found that the integrated process with the 1 kDa MWCO UF membrane yielded the best water quality that falls within the US EPA reuse standard for boiler-feed and cooling water. It was also observed that the permeate quality is fit for extended reuse as process water in the cement, petroleum and coal industries. In addition, the hybrid system’s operation consumed 37.13 Wh m−3 of energy at the highest applied pressure of 120 kPa, which is far lesser than the typical energy requirement range (0.8–1.0 kWh m−3) for such wastewater reclamation.

Pressure drop consideration has shown to be an essential requirement for the synthesis of a cooling water network where reuse/recycle philosophy is employed. This is due to an increased network pressure drop associated with additional reuse/recycle streams. This paper presents a mathematical technique for pressure drop optimization in cooling water systems consisting of multiple cooling towers. The proposed technique is based on the Critical Path Algorithm (CPA) and the superstructural approach. The CPA is used to select the cooling water network with minimum pressure drop while the superstructure allows for reuse of the cooling water. The proposed technique offers the opportunity to debottleneck the cooling water systems with multiple cooling towers while maintaining a minimum pressure drop. This technique, which was previously used in a cooling water network with a single source, has been adapted in a cooling water network with multiple sources. The mathematical formulations exhibit a mixed-integer nonl...

Most of the methodologies published in literature on wastewater minimisation for batch processes are based on short term scheduling techniques. When these methods are applied to longer time horizons, the computational time becomes intractable, hence the focus of this paper. This paper presents a methodology for simultaneous optimisation of production schedule and wastewater minimisation in a multipurpose batch facility. The key feature of the presented methodology is the adaption of cyclic scheduling concepts to wastewater minimisation. The methodology is developed based on continuous-time formulation and the state sequence network (SSN) representation. The methodology is successfully applied to two common literature examples and an industrial case study to demonstrate its effectiveness. None of the currently published wastewater minimisation techniques could solve the case study for a time horizon of 168 h. However, through the application of the presented methodology, a time horizon of 168 h for the case study was reduced to eight cycles with the cycle length of 23 h, for which the CPU time for the optimum cycle is 64.53 s.

This paper presents a mathematical technique for prediction of the optimal number of time points in short-term scheduling of multipurpose batch plants. The mathematical formulation is based on state sequence network (SSN) representation. The developed method is based on the principle that the optimal number of time points depends on how frequent the critical unit is used throughout the time horizon. In the context of this work, a critical unit refers to a unit that is most frequently used and it is active for most of the time points when it is compared to other units. A linear model is used to predict how many times the critical unit is used. In conjunction with knowledge of recipe, this information is used to determine the optimal number of time points. The statistical R 2 value obtained between the predicted and actual number of optimal time points in all the problems considered was 0.998, which suggests that the developed method is accurate in determining optimal number of time points. Consequently this avoids costly computational times due to iterations. In the model by Majozi and Zhu (2001) the sequence constraint that pertains to tasks that consume and produce the same state, the starting time of the consuming task at time point p must be later than the finishing time of the producing task at the previous time point p− 1. This constraint is relaxed by the proposed models if the state is not used at the current time point p . This relaxation gives a better objective value as compared to previous models. An added feature of the proposed models is their ability to exactly handle fixed intermediate storage (FIS) operational philosophy, which has proven to be a subtle drawback in published scheduling techniques.

Wastewater minimization can be achieved by employing water reuse opportunities. This paper presents a methodology to address the problem of wastewater minimization by extending the concept of water reuse to include a wastewater regenerator. The regenerator purifies wastewater to such a quality that it can be reused in other operations. This further increases water reuse opportunities in the plant, thereby significantly reducing freshwater demand and effluent generation. The mathematical model determines the optimum batch production schedule that achieves the minimum wastewater generation within the same framework. The model was applied to two case studies involving multiple contaminants and wastewater reductions of 19.2% and 26% were achieved.

Heat integration to minimise energy usage in multipurpose batch plants has been in published literature for more than two decades. In most present methods, time is fixed a priori through a known schedule, which leads to suboptimal results. The method presented in this paper treats time as a variable, thereby leading to improved results. Both direct and indirect heat integration are considered together with optimisation of heat storage size and initial temperature of heat storage medium. The resulting model exhibits MINLP structure, which implies that global optimality cannot generally be guaranteed. However, a procedure is presented that seeks to find a globally optimal solution, even for nonlinear problems. Heat losses from the heat storage vessel during idling are also considered. This work is an extension of MILP model of Majozi (2009), which was more suited to multiproduct rather than multipurpose batch facilities. Optimising the size of the heat storage vessel as well as the initial temperature of the heat storage fluid decreased the requirement for external hot utility for an industrial case study by 33% compared to using known parameters.

Recovery of low potential energy of flue gases, mainly from industrial boilers, has become one of the problems of interest in research. In this work, the contact economizer system is used to recover low potential heat from the gas turbine exhaust (flue gas) stream of a heat-integrated gasification combined cycle (IGCC) design of the Elcogas plant adopted from previous studies. The underlying support for this idea was the direct relationship between efficiency of the IGCC and the boiler feedwater temperature. Recovery of the flue gas heat to preheat the boiler feedwater was demonstrated to be capable of further increasing the thermal efficiency of the plant. The methodology developed is divided into two parts, i.e., determining the maximum boiler feedwater temperature attainable and applying Mickley’s graphical technique for dehumidification, following a slightly different procedure that allows for the calculation of the exact ratio between the liquid-phase heat-transfer coefficient and the gas-phase mass-...

Water minimization in the process industry is becoming increasingly important as environmental legislation becomes increasingly stringent and the awareness of the impact of industrial activities on the environment increases. Much work has been done on water minimization in continuous processes as evidenced by the detailed reviews of Bagajewicz (2000) and Foo (2009). Although water minimization for batch processes (batch water network in short) has been ignored in the past, it is steadily gaining more attention in research. An overview of the developments and methodologies proposed for batch water network is presented. The methodologies for water minimization can roughly be divided into insight-based and mathematical techniques. The former always consists of a two-step approach (targeting and design) in synthesizing a batch water network that features the minimum freshwater and wastewater flows for a given production schedule. The mathematical techniques, on the other hand, may be categorized into two subs...

The use of steam in heat exchanger networks (HENs) can be reduced by the application of heat integration with the intention of debottlenecking the steam boiler and indirectly reducing the water requirement [Coetzee and Majozi. Ind. Eng. Chem. Res. 2008, 47, 4405−4413]. By reducing the steam flow rate, the return condensate temperature to the boiler is compromised which adversely affects the boiler operation. A means of maintaining efficient boiler operation is to reheat the return flow to the boiler. Steam systems typically employ turbines of which the exhaust is frequently used as a heating utility in the background process. Since turbines operate at various steam levels, a means for incorporating these steam levels into the HEN optimization framework is necessary. Consequently this paper concerns the restructuring of all steam system heat exchangers using conceptual and mathematical analysis to create a series HEN with the aim of reducing the overall steam flow rate, while maintaining the boiler efficie...

The traditional steam system comprises a steam boiler and the associated heat exchanger network (HEN). Most research published in literature tends to address both the elements of the steam system as separate entities instead of analyzing, synthesizing, and optimizing the overall system in a holistic manner. True optimality of the steam system can only be achieved if the analysis is conducted within an integrated framework. Process integration has proven to be a powerful tool in similar situations. This paper presents a process integration technique for network synthesis using conceptual and mathematical analysis without compromising boiler efficiency. It was found that the steam flow rate to the HEN could be reduced while maintaining boiler efficiency by utilizing sensible heat from the high pressure steam leaving the boiler. In the event of too little sensible energy being available, a compromise in either minimum steam flow rate or boiler efficiency must be made. A dedicated preheater can also be added ...

Heat exchanger networks in steam systems are traditionally designed to operate in parallel. Coetzee and Majozi (Ind. Eng. Chem. Res. 2008, 47, 4405−4413) found that by reusing steam condensate with...

The integrated gasification combined cycle (IGCC) is an electrical power generation system which offers efficient generation from coal with lower effect on the environment than conventional coal power plants. However, further improvement of its efficiency and thereby lowering emissions are important tasks to achieve a more sustainable energy production. In this paper, a process simulation tool is proposed for simulation of IGCC. This tool is used to improve IGCC’s efficiency and the environmental performance through an analysis of the operating conditions, together with process integration studies. Pinch analysis principles and process integration insights are then employed to make topological changes to the flowsheet to improve the energy efficiency and minimize the operation costs. Process data of the Texaco gasifier and the associated plants (coal preparation, air separation unit, gas cleaning, sulfur recovery, gas turbine, steam turbine and the heat recovery steam generator) are considered as a base case, and simulated using Aspen Plus ® . The results of parameter analysis and heat integration studies indicate that thermal efficiency of 45% can be reached, while a significant decrease in CO2 and SOx emissions is observed. The CO2 and SOx emission levels reached are 698 kg/MWh and 0.15 kg/MWh, respectively. Application of pinch analysis determines energy targets, and also identifies potential modifications for further improvement to overall energy efficiency. Benefits of energy integration and steam production possibilities can further be quantified. Overall benefits can be translated to minimum operation costs and atmospheric emissions.

A novel operational policy, the Process Intermediate Storage operational policy, is introduced and used to synthesize, schedule and design multipurpose batch plants. The model is based on the State Sequence Network and non-uniform discretization of the time horizon of interest model developed by Majozi and Zhu [Majozi, T., Zhu, X. (2001). A novel continuous-time MILP formulation for multipurpose batch plants. 1. Short-term scheduling. Industrial and Engineering Chemistry Research, 40(23), 5935–5949]. Two cases are studied to determine the effectiveness of this operational policy. In the first case, which excludes any dedicated storage, the use of this operational policy results in 50% improvement in throughput. The second case is used to determine the minimum amount of intermediate storage while maintaining the throughput achieved with infinite intermediate storage. This results in 20% reduction in the amount of dedicated intermediate storage. The models developed for both cases are MILP models. An MINLP design model is then developed to exploit the attributes of the PIS operational policy.

This paper presents a methodology for wastewater minimisation in multipurpose batch plants characterised by multiple contaminant streams. Firstly a situation in which central reusable water storage does not exist is considered. In this case, water from one operation is directly reused in another operation as long as the source and sink operations, respectively, end and begin simultaneously. Secondly, the case with central reusable water storage is considered. In this case water from a source operation can temporarily be stored in dedicated storage before use by the sink process. The methodology is based on an existing scheduling framework which then makes it possible to generate the required schedule to realise the absolute minimum wastewater generation for a problem. The methodology involves a two-step solution procedure. In the first step the resulting MINLP problem is linearised and solved to provide a starting point for the exact MINLP problem.

Wastewater minimisation in batch plants is gaining importance due to intensifying environmental legislation and the gradual reduction in the number of freshwater sources. Intrinsic in the minimisation of wastewater in batch plants is the reuse of wastewater through intermediate storage vessels. However, the intermediate storage vessels take up unnecessary space which is undesirable in processes which are generally undertaken in limited spaces. Furthermore, in any batch process there are processing units that are not used extensively in the time horizon. In other words, these units remain idle for the major part of the time horizon, amounting to wasted return on capital investment. The idle processing units can be used as storage vessels, since any processing unit is, in essence, a storage vessel. In doing this one can reduce the size of the central storage and increase the utilisation of capital intensive processing units. The methodology presented in this paper deals with the minimisation of single contaminant wastewater by exploiting the inherent storage possibilities in idle processing units. The methodology is applied to two cases. In the first case the objective is to minimise the amount of effluent and the size of the central storage vessel through the usage of inherent storage, as commonly encountered in grassroot design. In the second case the objective is to determine the minimum wastewater target through the usage of both inherent storage and fixed central storage, as encountered in retrofit design.